Helicopter floating stabilator control system

ABSTRACT

Control system for a free floating stabilator for a helicopter having a control coupling to the longitudinal cyclic control linkage with provision for freeing the stabilator from controlled movement during flight operation such as hover so that the stabilator can assume a position providing minimum vertical drag.

United States Patent Albert 1March 20, 1973 HELICOPTER FLOATINGSTABILATOR CONTROL SYSTEM Aristide A. Albert, Stratford, Conn.

United Aircraft Corporation, East Hartford, Conn.

Filed: Nov. 10, 1971 Appl. No.: 197,253

Inventor:

Assignee:

U.S. Cl ..244/l7.l9, 416/98 Int. Cl ..B64c 27/04 FieldoISearch..244/l7.19,17.2l,17.23,17.25, 244/17.11, 17.13, 17.15, 17.17, 7A, 7 R, 90

[56] References Cited UNITED STATES PATENTS 2,630,985 3/1953 Sherry..244/17.l9 3,081,052 3/1963 Michel ..244/l7.19 3,105,659 10/1963 Stutz..244/17.19 X

Primary Examiner-Milton Buchler Assistant Examiner-Paul E. SaubererAtt0rneyRussell M. Lipes, Jr.

[57] ABSTRACT Control system for a free floating stabilator for ahelicopter having a control coupling to the longitudinal cyclic controllinkage with provision for freeing the stabilator from controlledmovement during flight operation such as hover so that the stabilatorcan assume a position providing minimum vertical drag.

8 Claims, 4 Drawing Figures FIGL-B FIG-4 PATENTEUmzoms SHEET 2 OF 2 illlHELICOPTER FLOATING STABILATOR CONTROL SYSTEM BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a flightcontrol system for a helicopter and more particularly to a system forfreeing a horizontal stabilizer or stabilator from controlled movementduring certain flight operation.

2. Description of the Prior Art In helicopter structures a horizontalstabilizer of some type may be employed to assist in providing stabilityto the aircraft and for maneuvering control. It is a usual practice forhelicopter manufacturers to attach stabilizers to the airframe body in afixed angle of attack relationship. The particular angle of attack maybe determined on the basis of experimentation or flight test for thenormal flight condition of the aircraft. Occasionally the mounting forthe stabilizer may include an adjustment feature whereby a mechanic onthe ground may loosen the mounting and adjust the stabilizer to adifferent position. While free floating or active-inactive horizontalstabilizers have been used in aircraft, an example being Auster et al.U.S. Pat. No. 2,712,420, there is a specific need in the flightoperation of a helicopter to provide a stabilizer which may be adjustedin forward flight in accordance with maneuverability control inputs madeby the pilot by means of the cyclic pitch control system and which alsocan be rotated for the hover mode of operation to a position where itoffers minimum air resistance or vertical drag and is disconnected fromthe control inputs. The requirement for the helicopter to achievegreater forward flight speeds while still retaining its capability toperform an efficient hover operation is the basis for this need.

SUMMARY OF THE INVENTION An object of the present invention is toprovide an improved helicopter flight control system.

Another object of the invention is to provide a helicopter flightcontrol system utilizing a horizontal stabilizer which has two phases ofoperation; one being in accordance with changes in rotor blade pitch andthe other being free floating with the stabilizer being positioned inaccordance with rotor downwash so as to offer minimum air resistanceduring certain helicopter maneuvering.

Still another object of the invention is to provide a helicopter flightcontrol system having a horizontal stabilizer which is directlycontrolled by the cyclic pitch stick and which may be selectivelydisengaged from cyclic pitch control so that it may seek a position ofminimum vertical drag with provision for restoring the stabilizer tocontrolled movement at will.

In accordance with the present invention, a helicopter is provided witha floating type horizontal stabilizer or stabilator, the position ofwhich can be adjusted during flight operation in accordance with cyclicpitch stick movements so that a tendency of the helicopter fuselage topitch up or down can be resisted and the fuselage can be kept level orin line with the plane of rotation of the rotor and thus reduce bendingloads. During hover operation, it is desirable to permit the stabilatorto be moved to a vertical position so that the downwash from the rotorwould have a minimum effect on the stabilator. It may be desirable toinclude in the cyclic pitch connection to the stabilator a trimcapability so that adjustments can be made for variations in the centerof gravity of the helicopter.

The foregoing and other objects, features and advantages of theinvention become more apparent in the light of the following detaileddescription of a preferred embodiment thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified schematicdrawing of a helicopter showing the stabilator structure in the tailarea.

FIG. 2 is an enlarged fragmentary portion of the rear of the helicopterof FIG. 1 showing the cyclic pitch linkage connection to the stabilatorin some detail.

FIG. 3 is an enlarged section through the stabilator showing details ofits coupling arrangement.

FIG. 4 is a circuit diagram of the hydraulic system for the stabilatorcontrol system.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, thehelicopter 10 is shown which has rotor 12 driven by one or more engineswithin compartment 4. The rotor has a plurality of blades 16, the pitchof which can be adjusted. Controls for the helicopter comprise normalhelicopter controls including cyclic pitch stick 18 in the pilotscompartment which is operatively connected to rotor blades l6..andwhich'is also connected to stabilator 20 as will be explained below. Thehelicopter also has tail rotor 22.

FIG. 2 shows in detail the coupling of the cyclic pitch control linkageto the stabilator. Cyclic pitch connector 24 is connected through trimactuator 26 and a series of bell cranks and rods such as bell crank 28and rod 30 to stabilator control actuator 32 which is essentially aservo. The trim actuator may be used for introducing adjustment to thecyclic pitch connection to compensate, for example, for changes in thelocation of the center of gravity of the helicopter. Rod 34 extendingfrom the control actuator is connected to floating crank 36 surroundingstabilator torque tube 38. This connection is also shown in FIG. 3. Thetorque tube is an integral part of the stabilator and its axis is theaxis about which the stabilator rotates.

Droop actuator 40 is pivotally anchored at its lower end and isconnected by piston rod 42 extending upward therefrom to fixed crank 44also surrounding torque tube 38 and having flange 46 connected to thetorque tube by one or more bolts 48 (F IG. 3). Floating crank 36actually surrounds fixed crank 44 and is journaled on flange 46. The twocranks 36 and 44 have a common axis of rotation with torque tube 38, andcrank 36 is capable of relative rotational movement with respect tocrank 44 and torque tube 38. Locking pin arrangement 50, indicated inFIG. 2, is provided for selectively locking cranks 36 and 44 together sothat they can rotate as a unit or selectively unlocking them so that onecrank can rotate with respect to the other. When the two cranks arejoined by the locking pin, position of stabilator 20 is adjusted inaccordance with longitudinal movement of cyclic pitch stick 18. Whenthey are not joined together, the stabilator is free to rotate about thetorque tube axis, and the downwash from rotor blades 16, as whenhelicopter is in a hover, will cause the stabilator to rotate in aclockwise direction until it assumes substantially a vertical position.

In the diagram of FIG. 4, high pressure fluid is admitted through line52 to the servo valve in stabilator control actuator 32 to provide themuscle for actuation of stabilator in response to cyclic pitch stickinputs through connector 24 or actuation of trim actuator 26. Duringsuch operation, no fluid pressure is applied to droop actuator 40 or tothe locking pin which is not shown in the figure but is understood to beoperatively connected to piston 54 in lock power cylinder 56. Thelocking pin, however, would be retained as through a spring loading in alock position so that floating crank 36 and fixed crank 44 are lockedtogether and the position of the stabilator is adjusted in accordancewith rotational movement of floating crank 36. Line 58 is a drain linefrom the servo in control actuator 32. The control actuator may alsohave separate fluid lines connecting it to automatic stabilizationequipment for automatic control of the stabilator position.

When it is desired to free stabilator 20 from cyclic pitch control sothat the stabilator can float and assume a free position, switch 60located in the pilot's compartment is actuated to position valve 62 toadmit fluid pressure from supply line 64 to line 66. This line isconnected to chamber 68 in the lower portion of lock power cylinder 56and the fluid pressure admitted there will act on the lower face ofpiston 54 to move the piston upward with resulting disengagement of thelocking pin holding cranks 36 and 44 together. Stabilator 20 then willbe free to assume a position in accordance with the aerodynamic loadsimposed thereon.

When the stabilator is floating and it is desired to bring it under thecontrol of the cyclic control system, switch 70 also located in thepilots compartment is actuated to position valve 62 to admit fluidpressure from supply line 64 to line 72. The line has flow regulator 74therein for reducing the pressure through the fluid lines downstream ofthat point to that required by the droop actuator 40. Branch line 76connects line 72 to the bottom end of droop actuator 40 so that pressurefluid admitted to chamber 78 within the actuator acts on the lower faceof piston 80. The chamber at the top side of the piston is vented.Branch line 82 is connected to chamber 84 at the top side of piston 54within lock power cylinder 56. Restriction 86 in branch line 82,downstream of the junction with branch line 76 delays the admission ofpressure fluid to chamber 84 when pressure fluid is admitted by valve 62to line 72 until after fluid pressure in droop actuator chamber 78 hasstarted to move piston 80 upward.

Both branch lines 76 and 82 are connected to drain line 88 which hasrelief valve 90 therein. This valve prevents an excessive pressurebuildup in the pressure fluid system after piston 80 through itsconnection with fixed crank 44 has moved stabilator 20 to a positionaligning the locking holes in floating crank 36 and fixed crank 44, andpiston 54 has moved the locking pin to a locked position. At the timethe locking pin has closed, a signal is transmitted to valve 62, causinga shift in valve position so as to shut off the admission of fluidpressure to line 72 and to vent that line and lines 76 and 82 to drainline 92. This will vent chambers 78 and 84,

to the drain line, and control of the position of stabilator 20 thenwill be in accordance with the cyclic pitch control system. In thefigure, valve 62 is schematically shown in this drain position.

Although the invention has been shown and described with reference to apreferred embodiment, it should be understood by those skilled in theart that the foregoing and other changes and omissions in the form anddetail thereof may be made therein without departing from the spirit andscope of the invention, which is to be defined and limited only as setforth in the following claims.

I claim:

1. A flight control system for a helicopter having a bladed rotor and astabilator:

cyclic means for controlling the pitch of said rotor blades;

means coupling said cyclic pitch controlling means and said stabilatorso that the position of said stabilator is adjusted in accordance withcyclic pitch; and

means for uncoupling said stabilator so that it is free floating.

2. The combination of claim 1 further including:

means for trimming said cyclic pitch controlling means.

3. A flight control system for a helicopter having a bladed rotor and astabilator;

cyclic means for controlling the pitch of said rotor blades;

first means operatively connected with said cyclic pitch controllingmeans;

second means operatively connected with said stabilator; and

means for selectively connecting together said first and second means sothat position of said stabilator is adjustable in accordance with cyclicpitch.

4. A stabilator for a helicopter having a bladed rotor:

said stabilator including a first crank fixedly connected thereto;

fluid pressure means for actuating said first crank and changing theposition of said stabilator; second crank means associated with saidstabilator; means for cyclic pitch control of said bladed rotor; meansconnecting said second crank means and said cyclic pitch control meansfor adjusting the position of said second crank;

means for locking said first and second crank means together;

fluid pressure means for actuating said locking means; means forunlocking said locking means when said first and second crank means arelocked together;

means for admitting fluid pressure to said first crank fluid actuatingmeans and to said locking means to lock said first and second crankmeans together; and

means for delaying admission of fluid pressure to said locking meansuntil fluid pressure is admitted to said first crank fluid actuatingmeans.

5. For a helicopter having a bladed rotor, a stabilator and cyclic pitchcontrol means;

a flight control system for said stabilator including;

first means connected to said stabilator;

means connected to said first means for moving said stabilator;

second means connected to said cyclic pitch control means;

means for locking said first and second means together so that saidstabilator can be moved in accordance with cyclic pitch inputs; and

means for selectively controlling the position of said stabilator inaccordance with cyclic pitch input, unlocking said locking means so thatsaid stabilator is unrestrained, and for returning said stabilator tothe control of cyclic pitch input.

6. For a helicopter having a bladed rotor, cyclic pitch control means,and a stabilator the position of which can be varied;

means for adjusting position of said stabilator in accordance withcyclic pitch;

means for freeing said stabilator from cyclic control so that it canassume a position in accordance with aerodynamic loads thereon; and

means for reestablishing cyclic pitch control of said stabilator when itis free floating.

7. The combination of claim 1 further including:

means for trimming the position of said stabilator as established bycyclic pitch.

8. In a helicopter having a stabilizer, a stabilizer inflight adjustmentsystem comprising an actuator connected to the stabilizer by a firstcrank member, a second crank member freely mounted on the stabilizeraxis adjacent the first crank member, a flight control linkage connectedto the second crank member, an engage disengage lock mounted tointerconnect said crank members, an actuator control valve, an unlockingswitch, and sequencing means between the actuator and the lock.

t l l

1. A flight control system for a helicopter having a bladed rotor and astabilator: cyclic means for controlling the pitch of said rotor blades;means coupling said cyclic pitch controlling means and said stabilatorso that the position of said stabilator is adjusted in accordance withcyclic pitch; and means for uncoupling said stabilator so that it isfree floating.
 2. The combination of claim 1 further including: meansfor trimming said cyclic pitch controlling means.
 3. A flight controlsystem for a helicopter having a bladed rotor and a stabilaTor; cyclicmeans for controlling the pitch of said rotor blades; first meansoperatively connected with said cyclic pitch controlling means; secondmeans operatively connected with said stabilator; and means forselectively connecting together said first and second means so thatposition of said stabilator is adjustable in accordance with cyclicpitch.
 4. A stabilator for a helicopter having a bladed rotor: saidstabilator including a first crank fixedly connected thereto; fluidpressure means for actuating said first crank and changing the positionof said stabilator; second crank means associated with said stabilator;means for cyclic pitch control of said bladed rotor; means connectingsaid second crank means and said cyclic pitch control means foradjusting the position of said second crank; means for locking saidfirst and second crank means together; fluid pressure means foractuating said locking means; means for unlocking said locking meanswhen said first and second crank means are locked together; means foradmitting fluid pressure to said first crank fluid actuating means andto said locking means to lock said first and second crank meanstogether; and means for delaying admission of fluid pressure to saidlocking means until fluid pressure is admitted to said first crank fluidactuating means.
 5. For a helicopter having a bladed rotor, a stabilatorand cyclic pitch control means; a flight control system for saidstabilator including; first means connected to said stabilator; meansconnected to said first means for moving said stabilator; second meansconnected to said cyclic pitch control means; means for locking saidfirst and second means together so that said stabilator can be moved inaccordance with cyclic pitch inputs; and means for selectivelycontrolling the position of said stabilator in accordance with cyclicpitch input, unlocking said locking means so that said stabilator isunrestrained, and for returning said stabilator to the control of cyclicpitch input.
 6. For a helicopter having a bladed rotor, cyclic pitchcontrol means, and a stabilator the position of which can be varied;means for adjusting position of said stabilator in accordance withcyclic pitch; means for freeing said stabilator from cyclic control sothat it can assume a position in accordance with aerodynamic loadsthereon; and means for reestablishing cyclic pitch control of saidstabilator when it is free floating.
 7. The combination of claim 1further including: means for trimming the position of said stabilator asestablished by cyclic pitch.
 8. In a helicopter having a stabilizer, astabilizer inflight adjustment system comprising an actuator connectedto the stabilizer by a first crank member, a second crank member freelymounted on the stabilizer axis adjacent the first crank member, a flightcontrol linkage connected to the second crank member, an engage /disengage lock mounted to interconnect said crank members, an actuatorcontrol valve, an unlocking switch, and sequencing means between theactuator and the lock.